This invention relates to electrical wiring systems utilizing flat conductor cables in lieu of conventional and round wiring systems, and to accessories employed therein.
More particularly, this invention relates to service modules or terminal boxes employed in flat conductor cable wiring systems.
Flat conductor cables, which comprise a plurality of conductive strips embedded in a thin insulating sleeve are finding increasing commercial use in the substitution or replacement of conventional and round wiring systems. By permitting wiring arrangements which may be placed under carpeting and tiling, flat conductor cable systems eliminate the need for extensive behind-the-wall electrical installations, the tacking of wiring to baseboards, and the inclusion of duct work in the walls and floors of buildings under construction which are meant to house conventional wiring systems. Thus, cable systems utilize the floor surface itself as the wiring bed.
Several under-carpet wiring systems have been offered commercially, one of which is the Flexway (trademark of Burndy Corporation) cable wiring system. In these systems, numerous and different types of cable connections are made which are analagous to the several types of connections performed in conventional wiring systems; that is, flat conductor cables are tapped, splice-connected to transition junctions, and connected to service modules or fittings. In a transition connection, a cable is mounted on and connected to an insulating member, from which connections are made to a conventional wiring system. Such transition junctions are normally contained within a conductive metal box or other enclosure which can be opened for access. A service module or fitting is a conductive box or other enclosure in which a flat conductor cable is again mounted and connected to an insulating member, from which power is tapped for direct use by the consumer. An example of this would be a terminal box in which the flat conductor cable is connected to an electrical wall outlet.
For safety considerations, the above mentioned cable systems are installed in three layers: a plastic insulating layer which directly contacts the surface on which the wiring system is to be laid; a middle layer which is the flat conductor cable itself; and a top grounding shield layer, typically comprised of a cold-rolled steel, which is used to ground the entire system. Generally, the lower most plastic insulating layer is of a thickness of several mils to about 25 mils; the thickness of the cable it self depends upon the exact gauge, but generally is of the order of 10 to 25 mils; and the upper grounding shield layer ranges in thickness between 5 and 15 mils. Therefore the total structure remains very thin despite the three-layered composite.
As before mentioned, flat conductor cables are comprised of a plurality of conductive strips which are separated from each other and insulated from each other by, and enclosed within, a thin insulating sleeve which is typically a plastic material, for example, polyester. The conductive strips are usually comprised of copper or a copper alloy, and the number of strips per cable can vary from several to a large number, depending upon the extensiveness of the wiring system contemplated. Taps, splices, transition connections and terminal connections are produced by clamping the conductive portion or portions of the cable or cables to be connected with electrically conductive connectors of various sorts. Squeeze-clamp connectors with teeth which penetrate the cable are in wide use, and a novel cable connection arrangement has been recently been introduced by the Burndy Corporation as part of the above referenced Flexway under-carpet wiring system. This electrical connection arrangement comprises the use of a hollow rivet connector which is made to penetrate the cable and be compressed into an eyelet shape which electro-mechanically secures the cable or cables. The apparatus and method of producing such a novel connection is described in detail in co-pending U.S. Pat. application Ser. No. 314,965 filed of even date, assigned to Burndy Corporation, entitled "Electrical Connection Apparatus and Procedure for Flat Conductor Cables and Other Similar Articles", the entire contents of which application are hereby expressly incorporated herein by reference.
When transition or terminal connections are to be made in a cable system, the cable portion to be tapped or connected is usually mounted on an insulating member which is further mounted within a service module accessible to an electrician. To produce such a connection, the top protective grounding shield is cut away, pulled back, or otherwise removed from the portion of the cable to be accessed. Therefore, with the cable thus mounted on an insulating member, it is clear because of the relative fragility of the constituants of the cable (that is, soft metal and plastic) that any stresses placed upon the module, such as movement of furniture over the wiring system or the general pushing and pulling which occurs when working with the system, could tend to damage the cable connection by pulling the cable away from the connectors and disrupting electrical service throughout the system. It would therefore be desirable to have, and it is a principal object of this invention to provide, a strain relief feature for flat cable conductor wiring system service modules which will prevent or reduce strain caused at the cable connection caused by the exertion of outside forces thereon.